1. Field of the Invention
The present invention relates to a method and a device for optimizing the orientation of a laser anemometer which is mounted on an aircraft, in particular a transport airplane, and which is intended for measuring the wind.
More particularly, although not exclusively, this laser anemometer is used to measure the wind when the aircraft is situated on the ground, in particular during a takeoff phase.
It is known that such a laser anemometer uses the frequency shift undergone by a monochromatic light wave, in particular a laser wave, when it is backscattered by aerosols (particles and/or molecules) present in the air. This shift makes it possible to determine the component of the wind speed vector along the sighting axis. More precisely, the laser anemometer emits a laser radiation at a predetermined distance of a few meters or of a few tens of meters beyond the aircraft and receives this laser radiation after backscattering by the air. The component of the speed vector along the laser sighting axis is directly related to the change of the wavelength of the laser radiation. Thus, by emitting three laser radiations in three different directions, the laser anemometer is capable of determining the three components of the wind speed vector.
2. Description of the Prior Art
A system for monitoring anemobaroclinometric parameters on an aircraft is known through the document WO-2007/036662. This monitoring system is intended to monitor the value of anemobaroclinometric parameters pertaining to the flight of the aircraft, namely parameters which are related to the position and to the speed of the aircraft in flight with respect to the surrounding air. This known monitoring system makes provision to use, in addition to standard measurement devices comprising known probes, at least one laser anemometer which is intended to measure a true speed parameter of the aircraft and which is mounted inside the structure of the aircraft. This known system is nevertheless intended solely for carrying out in-flight measurements. For its in-flight use, it exhibits numerous advantages, relative to the use of standard probes which are placed outside the aircraft, and in particular:
absence of drag and noise; and
much reduced sensitivity to ice and rain.
Moreover, it is known that it is also necessary to have accurate measurements of the wind on the ground, in particular for the operation of novel systems used on the ground, which are intended in particular to aid the piloting of the aircraft on takeoff.
There exists in particular a novel system intended to improve safety on takeoff. This system verifies that the preparation for takeoff (loading, performance calculation, systems initialization) and the takeoff itself (ground roll, alignment, acceleration) are carried out in a correct manner. Such a system for enhancing safety during takeoff, of TOS type (“Take-Off Securing”), exhibits in particular a function consisting in calculating the estimated distance required for takeoff, as a function of parameters of the aircraft and of the environment, and in comparing this estimated distance with the distance available. In this case, if the estimated takeoff distance is less than the length of the runway available, alerts are triggered to forewarn the pilot. This verification is carried out before the flight, as soon as all the necessary parameters have been inserted into the aircraft's flight management system, and/or at the start of the acceleration of the aircraft, by using the real values measured for some of these parameters.
A system, of TOM type (“Take-Off Monitoring”), which is intended to monitor, in real time, the acceleration of the aircraft on takeoff, is also known. Before takeoff, a theoretical profile of the ground speed, as a function of the distance traveled and of parameters to be inserted by the crew, is established with the aid of a model. During acceleration on takeoff, and up to a predetermined speed, the current profile of the ground speed (as a function of distance) is compared with this theoretical profile, and an alarm is triggered if insufficient performance is detected.
The previous systems, which are activated on the ground, use for their operation, as input to performance calculation models, wind and temperature data. Moreover, the monitoring system of TOM type also uses the true speed of the aircraft. Now, the accuracy and the integrity of the measurements of these parameters, carried out on the ground by a laser anemometer, are currently insufficient for it to be possible to use these measurements in the aforementioned performance calculations.